1. Field of the Invention
This invention relates generally to the sealing of flanged joints wherein ring seals are received within mating circular grooves to establish a fluid type seal between the flanges of a pressure containing system such as a piping system, a wellhead assembly, a pressurized vessel, etc. More particularly, the present invention concerns a system for sealing flanged joints and for detecting and maintaining the seal integrity thereof and provides means for monitoring the seal integrity of the joint seals and for pressure testing the joint seals prior to internal pressurization of the pipeline, wellhead, etc.
2. Description of the Prior Art
Many types of internally pressurized fluid handling systems such as pipelines, wellheads, pressure vessels and the like, are composed of structural sections having flanges at opposite extremities thereof which are secured in assembly by means of bolts that extend through the flanges. In order to establish sealing between the flanges, a circular sealing element is typically provided which is tapered at each extremity and which is received within opposed annular seal grooves formed in the flanges which have tapered side walls that are engaged by the tapered portions of the ring seal in order to establish sealing. FIGS. 2 and 3 of the drawings hereof identify standard ring seals which are commonly referred to as API ring seals. When properly installed, the opposed flanges are positioned in spaced relation and are drawn together about the metal ring seal with sufficient force to cause metal-to-metal sealing between the tapered surfaces of the ring seal and the tapered surfaces of the opposed seal grooves. As shown in FIG. 2, the sealing surfaces of the ring seal are merely in engagement with the tapered side walls of the seal grooves. As shown in FIG. 3, the flanges have been drawn together by means of bolts or clamps with sufficient force to cause the ring seal to induce metal deformation or coining of the side walls of the seal grooves and seal ring. Coining of the side walls of the ring typically occurs because the metal of the ring seals is typically of less hardness as compared to the metal structure defining the flanges.
It is well known in the industry that API ring seals can leak upon the occurrence of certain physical phenomena. Under circumstances where bolts are tightened to secure the flanges in sealed assembly, excessive heat or excessive pressure can cause sufficient bolt extension that the flanges are enabled to be moved part to a slight degree. When this occurs, there may be insufficient mechanical force between the ring seal and the corresponding side wall surfaces of the seal grooves to maintain a positive fluid tight seal. In this case, leakage will develop at the flanged joint. Under circumstances where flanged joints are made up to a very tight degree, metal coining will occur in a manner set forth in FIG. 3. After metal coining only slight movement of the flanges need occur before seal leakage will develop.
In some cases it may be desirable to separate a flanged joint having a ring seal of the nature set forth in FIGS. 2 and 3. Should this occur and a different seal ring be employed when the flanges are again brought into assembly, previous coining or scratching of the side wall surfaces of the seal grooves may prevent effective sealing by the replacement seal ring. It is desirable therefore to provide a ring seal having the general character of an API ring seal and which is capable of maintaining its sealed integrity under circumstances where slight flange movement occurs. It is also desirable to provide an API-type ring seal that may be effectively reused under circumstances where a flanged joint has been disassembled and is then reassembled. It is especially desirable to provide a ring seal which is capable of replacing a standard API ring seal and which contacts groove surface area for sealing which has not been contacted by the standard API ring seal. It is desirable also to provide a ring seal having the capability of self energized sealing due to differential taper in comparison to the taper of the seal grooves.
When API-type flanged joints are made up, typically the only way to test the sealing integrity thereof is to fully assemble the pressurized apparatus and then apply internal pressure up to a particular test level. If no leakage occurs, the assembled apparatus may then be placed in service. On the other hand, if leakage is detected, the leaking joint must be disassembled and then reassembled, after which pressure testing is again accomplished to determine seal integrity. Frequently, leakage of a single flanged joint may require complete disassembly of the joined apparatus in order that the leaking flange may be disassembled and then properly reassembled. In some cases, when leakage of a flanged joint is detected, operating personnel merely apply more force to the bolts or clamps of the flanged joint, thereby forcing the flanges into tighter engagement with the ring seal. This activity frequently causes excessive coining of the metal of the seal ring and flanges. If adequate sealing is not developed in this manner, the excessive coining that occurs during overstressing of the metal may require replacement of the ring seals, remachining of the seal grooves or replacement of the flanges. Assembly and pressure testing in this manner is an expensive and timeconsuming procedure and can cause significant loss of production thereby adding to the detrimental effect of the installation or repair procedure involved. It is desirable therefore to provide means for testing the sealed integrity of a flanged joint prior to internal pressurization of the pressure containing system.
Especially under circumstances where flanged joints become excessively heated, such as in the case of a fire, the bolts securing the flange in assembly can yield significantly to allow the development of seal leakage. Should seal leakage be detected, it is desirable to provide means for introducing supplementary or backup sealing, either selectively or automatically, to thus maintain or reestablish the seal integrity of the joint. It is also desirable to provide an API type ring seal having the capability of being pressure energized to enhance the sealing capability thereof.